An demand contract method is known as one of contract methods used for an electricity rate contract made between a shop or facility owner and a power company. In the demand contract method, a contract rate is determined in the following way. Specifically, an integration value of power consumption (hereinafter referred to as a power consumption integration value) is calculated for each predetermined time period (hereinafter referred to as a demand time period). Then, the contract rate is set based on the highest power consumption integration value among the power consumption integration values for the respective demand time periods in one year.
Here, the demand time period includes: time periods defined by a predetermined value such as 15 minutes or 30 minutes; time periods defined by a time zone set as having an increased amount of power consumption (12 to 2 o'clock, for example) and other time zones (2 to 4 o'clock, for example) according to the thus-set time zone; and time periods defined by time zones in which different electricity rates are applied. Shop or facility owners desire to keep the power consumption integration value for one demand time period at a low level.
To this end, demand control is performed. In the demand control, the power consumption integration value from a start to an end of a demand time period is predicted in the midcourse of the demand time period. Then, when the integration value thus predicted (hereinafter referred to a predicted integration value) exceeds a predetermined power target value, operation of a specific device is stopped. In general, the power target value is often set to a value equal to or below the highest power consumption integration value of the previous year. The power consumption integration value from the start to the end of the demand time period is conventionally predicted based on a linear predictive method.
The linear predictive method is performed based on the following arithmetic expression (1).R=P+(Δp/Δt)×Tn  (1),where R: a predicted value of power consumption from the start of a demand time period to the end of the demand time period    P: a power consumption integration value from the start of the demand time period to present time;    Δp: power consumption at sampling time;    Δt: sampling time; and    Tn: remaining time in the demand time period (time from the present time to the end of the demand time period).
In this method, however, if there is fluctuation of the value Δp/Δt, the predicted integration value R largely fluctuates as well. Particularly when the Tn has a large value, such fluctuation is apt to be significant. For this reason, in the conventional method, there is a possibility of adversely affecting the environment by stopping the operation of the device for a time longer than necessary or a possibility of causing the power consumption integration value to exceed contracted power by stopping the device at timing behind the optimal timing.
To address such a problem, there has been proposed an apparatus configured to register transitions of power consumption in respective demand time periods in a database in advance, to extract past data from the database, the past data indicating a transition of power consumption that is approximate to a transition of power consumption at sampling frequencies from the start to the present time in a current demand time period, and to predict a future power consumption transition from the extracted data (see Patent Document 1).
Meanwhile, apart from the foregoing, an apparatus for judging appropriateness of a power target value has been proposed. This apparatus is configured to detect and store a shutoff level attributable to demand control and duration of the shutoff level, then to calculate an accumulated time period of the shutoff durations in a predetermined period, and to determine the appropriateness of the power target value based on the accumulated time period thus calculated (see Patent Document 2).    Patent Document 1: JP-A 2002-27668    Patent Document 2: JP-B 3731110